In screen printing apparatus, objects such as containers are often rotated about a longitudinal centerline or turning axis through the article by a rotatable drive means such as a rotatable chuck. The articles need to be positioned with their turning axis aligned with the rotational axis of the chuck. Such alignment may be more easily obtained by machines which operate very slowly in contrast to high speed machines operated e.g. at 3000 to 5000 containers per hour. At higher speeds, the containers are shifted into and from the printing station in very short periods of time and the article may not be so precisely positioned as in machines which handle the objects very slowly and maintain the articles positioned more carefully. Because the misalignment of the turning axis of the object with the rotational axis of the chuck will result in improper printing on the object irrespective of the production rate at which the machine operates the present invention is useful with slow or semi-automatic machines such as shown in U.S. Pat. No. 4,282,806 as well as the fully automatic high production machine disclosed herein. In semi-automatic screen printing apparatus, such as shown in U.S. Pat. No. 4,282,806, the article to be printed may be loaded manually in a hopper and a container is transferred by a single transfer arm directly from the hopper to the printing station. The printing head carrying the screen is raised to accommodate feeding of the object into a chuck which automatically rotates the object to a reference position for initiation of printing. A rack and pinion drive rotate the chuck and the object in timed relationed to movement of the screen relative to a stationary screen and flood bar. After printing, the object is removed manually and sent to a UV curing operation. One problem with such semi-automatic equipment is that it is relatively slow in production. A considerable portion of the cycle is spent in raising and in lowering the printing head and in turning the container to its reference position.
Silk screen printing apparatus disclosed in the aforementioned patent may be set up rather quickly to handle various diameters of containers. When changing sizes of containers, the rotational velocity of container surface is matched to the linear velocity of the screen by changing the size of the gear driven by the rack. Also, the nest or container receiving pocket on the transfer arm is changed where the difference in container diameter is quite large. Such set up time is relatively simple and easily accomplished as contrasted to existing conventional fully automated equipment used for silk screening apparatus.
More specifically, a known silk screen printing apparatus of the automated kind employs a walking beam transfer mechanism which has a number of container receiving grooves or notches therein to hold a series of containers each being moved incrementally toward the printing station. Such a system is difficult to set up for different sizes of containers or for different objects. The change of size of the walking beam and the adjustments of the movement thereof, as well as to change the rotational speeds, has resulted in many hours of set up time being required for substantial changes in container diameters. Furthermore, the articles are jostled as they are moved step by step by the walking beam and the articles may be marked or marred by such movement. There is a loss of accuracy of container position with such a walking beam. Often this walking beam printing equipment is not able to be quickly converted from cylindrical containers to other container shapes such as oval or conical.
Thus, there is a need in the industry for an automatic screen printing apparatus that may be readily set up to handle each of several sizes as well as shapes of containers. For instance, some users may change from a one ounce container to a quart container, and from a cylindrical to an oval container, and they desire that the set up time for the changeover be similar to that used for semi-automatic screen printing apparatus of U.S. Pat. No. 4,282,806.
In addition to having shortcomings in handling various sizes and shapes of containers, existing automatic screen printing apparatus is complicated and expensive. The walking beams and chain conveyors used heretofore for article feeding and handling involved considerable mass and momentum to be overcome in each printing and feeding cycle. When using a large number of moving parts, the adjustments thereof, the tolerance buildups and the multiple adjustments necessary to obtain the desired position of registration of the printed material on the container are time consuming. Furthermore, large chain conveyors or walking beam conveyors add considerable to the expense of the automatic screen printing apparatus relative to semi-automatic screen printing apparatus.
The present invention is particularly useful when handling articles such as containers or bottles at very high rates of production, e.g. 4000 containers per hour. In such equipment, the containers are fed automatically from incoming supply conveyor to the printing station at which the container's axis of turning must be aligned with the axis of rotation of the chuck. The chuck turns the container as the printing progresses about the circumferential surface of the container. When the container's axis is not aligned with the chuck axis, inferior or poor printing results. Thus, there is a need to provide container and chuck alignment means on such high production screen printing apparatus which means is highly reliable and consistent in its operation. A need also exists to remove the printed articles automatically from the chuck at these same high production rates and to discharge the articles to a conveying means, which may be a conveyor leading to and through a UV curing apparatus for a UV ink applied to the containers.
Accordingly, a general object of the invention is to provide a new and improved article and chuck axis alignment in a screen printing apparatus.
Another object of the invention is to provide an automatic screen printing apparatus with improved article handling and positioning means to position articles consistently in alignment with the rotational axis of a rotating chuck with simple and inexpensive equipment.
These and other objects and advantages of the invention will become apparent from the following description of the invention taken in connection with the accompanying drawings.